Method and apparatus of recording/reproducing multi-channel stream

ABSTRACT

The present invention relates to multi-channel stream recording/reproducing method and apparatus. The present multi-channel stream reproducing method checks whether or not reproduced multi-channel stream belongs to same broadcast (RF) channel, and deletes PSI (Program Specific Information) packets included in channel stream excluding one channel stream if it belongs to same RF channel, and makes new PSI packets with reference to PSI packets included in reproduced multi-channel stream to replace them, if not. Furthermore, the present method compensates appropriately PCRs (Program Clock References) included in channel stream excluding one channel stream in case of the latter. The present method enables a digital TV set to present multi-channel stream simultaneously in PIP (Picture-In-Picture) or multi-screen mode with no error in channel selection and presentation (or decoding) time.

TECHNICAL FIELD

The present invention relates to method and apparatus thatrecords/reproduces a multi-channel stream to/from a recording mediumsuch as a high-density DVD (Digital Versatile Disk).

BACKGROUND ART

Owing to technical improvement in the fields of video/audio datacompression, digital modulation/demodulation, and so on, a digitaltelevision broadcast system broadcasting TV signals in the form ofdigital data stream is being standardized rapidly.

In the digital television broadcast system, audio/video (A/V) signals tobe broadcasted are compressed according to the data compressing rulespecified by MPEG 2 (Moving Picture Experts Group) and the compressedA/V data are broadcasted in the form of transport stream (TS), which isalso defined in MPEG 2 standard, composed of successive 188-byte-longtransport packets (TPs).

The digital TV broadcast system, which will be commercialized soon owingto technical improvement of A/V data compression and transmission, isable to support much higher-quality of video and audio than an analog TVsystem. Furthermore, it ensures data compatibility with a digitalcommunication device, a digital storage device, etc.

By the way, a new device is being developed to prepare forcommercialization of digital TV broadcast system. That is a digitalrecorder being able to receive TS of digital broadcast programs and torecord it on a writable HD-DVD. Such a digital recorder will be widelyused as the digital TV broadcast system is commercialized in earnest.

A single physical broadcast channel (called ‘RF channel’ in general) hasabout 6 MHz bandwidth which ensures 19.4 Mbps data rate. This data ratecan carry a single HD-TV broadcast signal or about four SD-TV signals.Such a logical or virtual channel carrying one SD-TV signal in an RFchannel is called ‘sub-channel’.

In other words, a single RF channel sometimes includes several digitalchannels, namely, sub-channels which carry mutually-different broadcastprograms. Therefore, a DVD recorder being developed must be able torecord/reproduce two or more sub-channels simultaneously at a user'srequest. In addition, it may be able to record/reproduce two or moresub-channels chosen from different RF channels, respectively.

By the way, an apparatus being able to receive and present digital TVbroadcast programs, e.g., a digital TV set can not select a sub-channeland decode a received RF stream until PSI (Program Specific.Information) for a digital stream of TV program is received. Moreover,it can keep an exact presentation timing of packets constituting adigital stream after synchronizing an internal clock with PCRs (ProgramClock Reference) where respective PCRs carried by the digital stream arereceived within an allowable interval.

In general, a digital recorder records one channel and reproduces itlater. In case that a digital recorder is able to record a plurality ofchannels, it may reproduce one channel chosen among recorded channels,or reproduce at least two channels simultaneously to present them in amulti-screen, e.g., PIP (Picture-In-Picture) on a digital TV set.

In this multi-channel providing, PSI providing way must bedifferentiated and PCRs inserted in each channel stream may becompensated depending upon whether all multi channels belong to a singleRF channel or not.

DISCLOSURE OF INVENTION

It is an object of the present invention to provide a PSI recordingmethod for a plurality of channels that records PSI about a plurality ofrecorded channels to enable later individual or simultaneouspresentation of the recorded channels on a display machine such as adigital TV set.

It is another object of the present invention to provide a PSItransmitting method that transmits PSI recorded along with a pluralityof channels to enable later simultaneous presentation thereof on adisplay machine such as a digital TV set.

It is another object of the present invention to provide atime-information providing method that provides time information of aplurality of recorded channels to enable later simultaneous presentationthereof on a display machine such as a digital TV set.

A method of recording a multi-channel stream in accordance with thepresent invention is characterized in that it selects a plurality ofsub-channels from a tuned broadcast channel, copies PSI packets includedin a stream of the tuned broadcast channel into every stream of theselected plural sub-channels if the plurality of sub-channels are insame broadcast channel, records the sub-channels onto a recordingmedium, and writes information on whether the recorded sub-channelsbelong to same broadcast channel or not.

A method of reproducing a multi-channel stream in accordance with thepresent invention is characterized in that it checks whether a pluralityof channels reproduced from a recording medium belong to same broadcastchannel or not, removes PSI packets included in a channel or channelsexcept one channel if the plural channels belong to same broadcastchannel, reconstructs new PSI packets based on information of PSIpackets included in respective stream of said channels to replace theexisting PSI packets and compensates PCRs adequately if the pluralchannels belong to different broadcast channels, and multiplexes thestream of the plural channels to output.

The above-characterized multi-channel stream recording/reproducingmethod can provide a digital display machine set with PCRs and PSIsuitable for a plurality of sub-channels chosen from one RF channel ormutually-different RF channels, thereby eliminating errors in channelselection or presentation timing in a digital display machine.Consequently, multi-screen, e.g., PIP displaying is ensured throughstable decoding of multi channels.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of a disk device to record a multi-channelstream in accordance with the present invention;

FIG. 2 illustrates a schematic process to select two sub-channels from asingle RF (broadcast) channel to record onto a recording medium;

FIGS. 3 a and 3 b show different types of a specific field of programinformation associated with a recorded stream;

FIG. 4 illustrates a schematic process to select two sub-channels fromtwo different RF channels to record onto a recording medium;

FIG. 5 is a block diagram of a disk device to reproduce a recordedmulti-channel stream in accordance with the present invention;

FIG. 6 illustrates a schematic process to reproduce two sub-channelsbelonging to same RF channel that were recorded by the recording processof FIG. 2;

FIG. 7 illustrates a schematic process to reproduce two sub-channelsbelonging to different RF channels that were recorded by the recordingprocess of FIG. 4; and

FIGS. 8 a to 8 c show exemplary manners to compensate PCRs of areproduced multi-channel stream in accordance with the presentinvention.

MODES FOR CARRYING OUT THE INVENTION

In order that the invention may be fully understood, a preferredembodiment thereof will now be described with reference to theaccompanying drawings.

FIG. 1 is a block diagram of a device to record a multi-channel streamin accordance with the present invention. The device of FIG. 1, whichmay be a digital video recorder (DVR) being able to record onto awritable HD-DVD (High-Density DVD), comprises two tuners 10 and 20tuning their respective passbands to an RF band of digital broadcast TVsignal; two PCR/PSI decoders 11 and 21 extracting packets containing PCRand PSI from a digital stream of RF channels chosen respectively by thetwo tuners 10 and 20; two stream selectors 12 and 22 selecting asub-channel respectively from a digital stream outputted through thePCR/PSI decoders 11 and 21; two clock counters 14 and 24 generatingindividual clocks, synchronizing their clocks with corresponding PCRsextracted by the PCR/PSI decoders 11 and 21, and counting thesynchronized clocks; two buffers 13 and 23 storing TPs (TransportPackets) constituting each sub-channel stream while adding counts in theclock counters 14 and 24 to each TP whenever it is arrived; a streamwriter 15 writing packets stored in the two buffers 13 and 23alternately, and creating and writing navigation data for the stream tobe written; an optical pickup 16 forming mark/space patterns or pits ona recording medium 100 such as an HD-DVD in accordance with bit patternsof stream and navigation data outputted from the stream writer 15; and acontroller 17 conducting overall control operations of all elements formulti-stream record.

Each of the two tuners 10 and 20 passes one digital broadcast TVchannel, namely, an RF channel selected by the controller 17, and eachof the two PCR/PSI decoders 11 and 21 extracts packets containing a PCRand PSI packets that have segmentized PSI for a broadcast program. Atleast one PCR has been inserted in a digital stream of an RF channel atlongest within an allowable interval, e.g., 100 msec specified bydigital TV broadcast standard. The PCR/PSI decoders 11 and 21 send PCRsincluded in the extracted packets to the clock counters 14 and 24,respectively.

Each of the stream selectors 12 and 22 watches PID (Packet ID) of everyTP constituting a received digital stream of an RF channel, and outputsonly TPs of which PID is corresponding to each sub-channel chosen by thecontroller 17.

Each of the two clock counters 14 and 24 synchronizes its own clock withsuccessively-received PCRs, keeps counting the synchronized clock, andprovides a clock count for each of the buffers 13 and 23 as a PAT(Packet Arrival Time).

Each of the buffers 13 and 23 reads a count of the clock counter 14 or24 whenever a TP is stored and adds the read count to the stored TP as aPAT. Thusly-stored TPs with PAT are retrieved in a predetermined dataunit alternately from the buffers 13 and 23 by the stream writer 15 andthen applied to the optical pickup 16 to be written on the HD-DVD 100.The stream writer 15 also creates and writes navigation data for thewritten stream during or after record of the stored TPs in the buffers13 and 23.

Through the above-explained process, two sub-channels chosenrespectively from different RF channels are recorded on the HD-DVD 100.

Two sub-channels may be chosen from a single RF channel. In this case,the first stream selector 12 selects not one but two sub-channels. Oneof the selected two sub-channels is transmitted into the second buffer23 that uses a count of not the second clock counter 24 but the firstclock counter 14 to add PAT to each stored TP. Thusly-stored TPs of twosub-channels of same RF channel are retrieved alternately from thebuffers 13 and 23 by the stream writer 15 and then written on the HD-DVD100, in the same manner explained above.

The briefly-described method of recording a plurality of sub-channelschosen from a single or multi RF channels onto a recording medium isexplained in detail below.

FIG. 2 illustrates a schematic process to select two sub-channels from asingle RF channel to record them onto a recording medium. In the exampleof FIG. 2, the sub-channels CH1 and CH3 are selected from a single RFchannel tuned by the first tuner 10 containing four sub-channels of SDquality according to a viewer's selection.

The two sub-channels selected by the first stream selector 12 are storedseparately into the first 13 and the second buffer 23. At this time, thefirst stream selector 12 inserts PSI packets extracted by the firstPCR/PSI decoder 11 into one sub-channel and copies those packets intothe other sub-channel to make both sub-channels stored in the twobuffers 13 and 23 have same PSI packets.

Both of the buffers 13 and 23 read a clock count of the first clockcounter 14 and add to each TP of each sub-channel when it is stored. Theseparately-stored stream 201 and 202 of two sub-channels are alternatelyretrieved in a predetermined data unit by the stream writer 15 and thenwritten onto the HD-DVD 100.

The stream writer 15 writes the two sub-channels in a single streamobject, which is a management unit, or in two different stream objectsand creates and records navigation data for each stream object.

According to the standard of a high-density recording medium, a singlepiece of PGI (ProGram Information) is associated with a single streamobject. For preparing the case that a plurality of sub-channels arerecorded in a single stream object, the program-type field ‘PG_TY’, oneof fields of PGI associated with the stream object, has a 3-bitsub-field ‘Channel_Ns’ indicative of sub-channel recorded type, as shownin FIG. 3 a.

This sub-field ‘Channel_Ns’ is ‘000’ when one sub-channel stream isrecorded in a single associated stream object, ‘001’ when twosub-channels from same RF channel are recorded, and ‘010’ when twosub-channels from different two RF channels are recorded.

Thus, ‘001’ is written in the sub-field ‘Channel_Ns’ for themulti-channel stream recording example of FIG. 2.

If each sub-channel is recorded in a single stream object so that pluralpieces of PGI are created, the program-type field ‘PG_TY’ may have theformat of FIG. 3 b. The sub-field of linked program number ‘LK_PG_Nu’given in FIG. 3 b is 4-bit long. This sub-field is ‘0XXX’ when a singlechannel is recorded. b3 and b2 are ‘1’ and ‘0’ respectively, and a valueof ‘the other channel number−1’ is written in bits of b1b0 when twosub-channels belonging to same RF channel are recorded simultaneously.b3b2 is ‘11’ and b1b0 have a value of ‘the other channel number−1’ whentwo sub-channels belonging to different RF channels are recordedsimultaneously.

Thus, in case of the multi-channel stream recording example of FIG. 2,‘1010’ is written in the sub-field ‘LK_PG_Nu’ of PGI associated with astream object in which the sub-channel CH1 has been written, and ‘1000’is written in that field of PGI associated with another stream object inwhich the sub-channel CH3 has been written.

Those sub-fields ‘Channel_Ns’ and ‘LK_PG_Nu’ can be allocated in anothernavigation data, e.g., cell information instead of PGI.

FIG. 4 illustrates a schematic process to select two sub-channels fromtwo different RF channels to record them onto a recording medium. In theexample of FIG. 4, the sub-channel CH1 of SD quality is selected by thefirst stream selector 12 from a RF channel tuned by the first tuner 10,and the sub-channel CH3 of SD quality is selected by the second streamselector 22 from another RF channel tuned by the second tuner 20.

In case that two selected sub-channels belonging to different RFchannels are recorded as above, the two stream selectors 12 and 22insert PSI packets ‘PSI1’ and ‘PSI2’, which are extracted from differentRF channels respectively by the PSI/PCR decoders 11 and 21, in theselected sub-channels respectively and then send the PSI packet-insertedsub-channels to the buffers 13 and 23. The first buffer 13 reads a4-byte current count of the first clock counter 14 and adds the readcount to the received TP of the sub-channel CH1 as PAT thereof. Thesecond buffer 23 reads a 4-byte current count of the second clockcounter 24 to add to the received TP of the sub-channel CH3 from thesecond stream selector 22.

The sub-channels CH1 401 and CH3 402 stored respectively in the first 13and the second buffer 23 are recorded in a single stream object or intwo stream objects separately on the HD-DVD 100 as explained above.Navigation data related with a created stream object or stream objectsare also created by the stream writer 15 and then recorded onto therecording medium 100.

If the program-type field of FIG. 3 a is adopted for the recordingexample of FIG. 4, ‘010’ is written in the sub-field ‘Channel_Ns’, andif the program-type field of FIG. 3 b is used, ‘1110’ is written in thesub-field ‘LK_PG_Nu’ of PGI for the stream 401 of sub-channel CH1.

A reproducing method and apparatus of reproducing a multi-channel streamrecorded as above is explained below.

FIG. 5 is a block diagram of a disk device to reproduce a recordedmulti-channel stream in accordance with the present invention. Thedevice of FIG. 5, which may be a digital video recorder (DVR) ,comprises a stream reader 36 reading recorded signals, processing theread signals to restore original data stream, and separating therestored data stream into individual sub-channel stream; two buffers 33and 35 storing the separated sub-channel stream; two PCR/PSI decoders 32and 34 separating each sub-channel stream into PCR information, PSIpackets, and real data, namely, A/V (Audio/Video) packets; a clockcounter 30 counting an internal clock continuously; a re-multiplexer 31constructing a multi-channel stream newly, if needed, from thesub-channel stream outputted respectively through the two PCR/PSIdecoders 32 and 34 based on how the sub-channels are related each other;and a controller 37 controlling the stream constructing operation of there-multiplexer 31 after checking how the reproduced sub-channels arerelated each other.

A multi-channel stream reproducing method conducted by the device ofFIG. 5 is explained in detail below.

The stream reader 26 reads a multi-channel stream that is recorded in asingle stream object or separately in two stream objects. If it is readfrom a single stream object, the stream reader 26 reads recorded datasequentially and separates into respective sub-channels based on PID ofeach TP, and if from two stream objects, the stream reader 26 reads twostream objects alternately and stores alternately-read data in thecorresponding buffer 33 or 35.

The stream reader 26 also checks the program-type field of PGIassociated with a single or plural stream objects, and notifies thecontroller 37 of a value of the sub-field ‘Channel_Ns’ shown in FIG. 3 aor the sub-field ‘LK_PG_Nu’ shown in FIG. 3 b. Then, the controller 37knows, based on the notified information, how the read-out sub-channelsare related each other and controls the re-multiplexer 31 according tothe known fact.

Each sub-channel stream stored in the buffers 33 and 35 is separatedinto PSI packets and A/V packets by the PSI/PCR decoder 32 or 34, andeach PCR written in a TP is decoded and then delivered to there-multiplexer 31. The re-multiplexer 31 processes input of the twosub-channels differently based on the control information from thecontroller 37.

FIG. 6 illustrates a schematic process to reproduce two sub-channelsbelonging to same RF channel that were recorded as the exemplaryrecording process of FIG. 2.

In the example of FIG. 6, the controller 37 knows that the reproducedsub-channels belong to same RF channel based on a fact that thedelivered sub-field value from the stream reader 36 is ‘001’ in‘Channel_Ns’ or ‘1000’ or ‘1010’ in ‘LK_PG_Nu’. Thus, the controller 37applies a signal indicative of ‘same channel mode’ to the re-multiplexer31.

Then, the re-multiplexer 31 removes PSI packets inserted in onesub-channel stream of the two, e.g., the sub-channel stream from thesecond PSI/PCR decoder 34 because the two reproduced sub-channels havesame PSI packets. One sub-channel stream and the other sub-channelstream from which PSI packets are removed are stored temporarily in aninternal buffer of the re-multiplexer 31. TPs of the two sub-channelsstored together in the internal buffer are multiplexed to be transmittedsequentially in order of PAT thereof. Namely, a TP with preceding addedPAT is transmitted a head of a TP with later PAT regardless ofsub-channel thereof.

After transmission of the first TP, the next TP is transmitted themoment the count difference between a current count of the clock counter30 and a previous count when the first TP was transmitted is equal tothe time difference between PAT of the next TP and the PAT of the firstTP already transmitted. Each transmitting time of next successive TPs isdetermined in the same manner.

A displaying machine such as a digital TV set receiving the stream oftwo sub-channels transmitted as above can select and decode it based onPSI information to present in multi-screen or in PIP screen.

FIG. 7 illustrates a schematic process to reproduce two sub-channelsbelonging to different RF channels that were recorded as the exemplaryrecording process of FIG. 4.

In the example of FIG. 7, the controller 37 knows that the reproducedsub-channels belong to mutually-different RF channels based on a factthat the delivered sub-field value from the stream reader 36 is ‘010’ in‘Channel_Ns’ or ‘1100’ or ‘1110’ in ‘LK_PG_Nu’. Thus, the controller 37applies a signal indicative of ‘different channel mode’ to there-multiplexer 31.

Then, the re-multiplexer 31 examines the PSI packets ‘PSI1’ and ‘PSI2’included respectively in the two sub-channels inputted from the PSI/PCRdecoders 32 and 34 to construct new PSI packets ‘PSIn’ accordingly. Theold PSI packets ‘PSI1’ and ‘PSI2’ are individually replaced with thesenew PSI packets ‘PSIn’. PSI information carried by the new PSI packetsincludes PAT (Program Association Table), PMT (Program Map Table), NIT(Network Information Table), and CAT (Conditional Access Table) that aremade in view of a virtual single RF channel composed of the sub-channelsCH1 and CH3.

And, PCRs are also modified to make a virtual single RF channel out ofthe two sub-channels having belonged to different RF channels. For themodification of PCRs, the re-multiplexer 31 calculates a PCR offset thatis necessary to add to or subtract from PCRs carried by eithersub-channel of the two. The PCR offset is equal to a difference betweenthe first PCRs of the two sub-channels.

For example, if the first PCR ‘PCR31’ of the sub-channel CH3 of thesecond RF channel is ‘900’ and the first PCR ‘PCR11’ of the sub-channelCH1 of the first RF channel is ‘1000’, as shown in FIG. 8 a, then thePCR offset is ‘100’.

The PCR offset obtained as above is added to each PCR ‘PCR3x’ of onesub-channel stream of which the first PCR is smaller, namely, thesub-channel stream CH3, or is subtracted from each PCR ‘PCR1x’ of whichthe first PCR is larger, namely, the sub-channel stream CH1. FIGS. 8 band 8 c show respective cases that the sub-channel CH3 is compensated inits individual PCRs.

Another time information such as PTS (Presentation Time Stamp) and DTS(Decoding Time Stamp) carried by a sub-channel stream whose PCRs aremodified is also modified by the PCR offset.

TPs of the two sub-channels reconstructed as above are multiplexed to betransmitted sequentially in order of PAT thereof. The transmittinginterval among successive TPs is determined the same as explainedbefore.

A displaying machine such as a digital TV set receiving themulti-channel stream transmitted as above can select and decode it basedon PSI information to present in multi-screen or in PIP screen.

In case that two sub-channels that have been recorded during differenttime zone are reproduced simultaneously, even though they are in same RFchannel, the above-explained reproducing method for sub-channelsbelonging to different RF channels is applied instead of the method forsub-channels belonging to same RF channel.

In other words, PCRs (PTS/DTS as well) of one sub-channel are modifiedand PSI information is reconstructed before they are provided for adigital TV set, in this case. Furthermore, because their respectiverecording time zones are different, PATs of one sub-channel stream ofwhich the first PAT is precedent are all added by the difference betweenthe two first PATs. And, transmitting sequence and interval among TPs ofthe two sub-channels are determined based on the modified PATs of theone sub-channel and the original PAT of the other.

The invention may be embodied in other specific forms without departingfrom the sprit or essential characteristics thereof. The presentembodiments are therefore to be considered in all respects asillustrative and not restrictive, the scope of the invention beingindicated by the appended claims rather than by the foregoingdescription and all changes which come within the meaning and range ofequivalency of the claims are therefore intended to be embraced therein.

1-24. (canceled)
 25. A method of reproducing video data recorded in arecording medium, comprising: reading navigation information from therecording medium, the navigation information comprising informationindicating a presence of a video stream for displaying a PIP(Picture-In-Picture); and reproducing a first video stream and the videostream for displaying a PIP simultaneously based on the navigationinformation.
 26. The method of claim 25, wherein the first video streamand the video stream for displaying a PIP are separate.
 27. The methodof claim 25, further comprising reproducing the video stream fordisplaying a PIP when the navigation information indicates the presenceof the video stream for displaying the PIP.
 28. The method of claim 25,wherein the first video stream and the video stream for displaying a PIPare reproduced in a single stream object.
 29. The method of claim 28,wherein the navigation information comprises navigation data for thesingle stream object.
 30. The method of claim 25, wherein the firstvideo stream and the video stream for displaying a PIP are reproducedseparately in two different stream objects.
 31. The method of claim 30,wherein the navigation information comprises navigation data for each ofthe two different stream objects.
 32. A method of recording video dataon a recording medium, comprising: recording a first video stream and asecond video stream on the recording medium, the second video stream fordisplaying a PIP (Picture-In-Picture); and recording navigationinformation on the recording medium, the navigation informationcomprising information indicating the presence of the second videostream.
 33. The method of claim 32, wherein the first video stream andthe second video stream are recorded separately.
 34. The method of claim32, wherein the first video stream and the second video stream arereproduced in a single stream object.
 35. The method of claim 34,wherein the navigation information comprises navigation data associatedwith the single stream object.
 36. The method of claim 32, wherein thefirst video stream and the second video stream are recorded separatelyin two different stream objects.
 37. The method of claim 36, wherein thenavigation information comprises navigation data for each of the twodifferent stream objects.
 38. A recording medium, the recording mediumcomprising: a first video stream and a second video stream, the secondvideo stream for displaying a PIP (Picture-In-Picture); and navigationinformation comprising information indicating the presence of the secondvideo stream.
 39. The recording medium of claim 38, wherein the firstvideo stream and the second video stream are stored in a single streamobject.
 40. The recording medium of claim 38, wherein the navigationdata comprises navigation data associated with the single stream object.41. The recording medium of claim 40, wherein the first video stream andthe second video stream are stored separately in two different streamobjects.
 42. The recording medium of claim 41, wherein the navigationinformation comprises navigation data for each of the two differentstream objects.
 43. An apparatus for reproducing video data recorded ina recording medium, the apparatus comprising: a reproducing unit forreproducing data from the recording medium; and a controller forcontrolling the reproducing unit to read navigation information from therecording medium, and controlling the reproducing unit to reproduce afirst video stream and a video stream for displaying a PIP(Picture-In-Picture) simultaneously based on the navigation information,wherein the navigation information comprises information indicating apresence of the video stream for displaying the PIP.
 44. The apparatusof claim 43, wherein the controller further controls the reproducingunit to reproduce the video stream for displaying a PIP when thenavigation information indicates the presence of the video stream fordisplaying the PIP.
 45. The apparatus of claim 43, wherein thereproducing unit further reads a single stream object from the recordingmedium, the single stream objecting comprising the first video streamand the video stream for displaying the PIP.
 46. The apparatus of claim45, wherein the controller further controls the reproducing unit toreproduce the single stream object based on navigation data for thesingle stream object.
 47. The apparatus of claim 43, wherein thereproducing unit further reads two stream objects from the recordingmedium, wherein one of the two stream objects comprises the first videostream and the second of the two stream objects comprises the videostream for displaying the PIP.
 48. The apparatus of claim 47, whereinthe controller further controls the reproducing unit to reproduce thetwo stream objects based on navigation data for each of the two streamobjects.
 49. An apparatus for recording video data on a recordingmedium, the apparatus comprising: a recording unit for recording data onthe recording medium; a controller for controlling the recording unit torecord a first video stream and a second video stream for displaying aPIP (Picture-In-Picture) on the recording medium and controlling therecording unit to record navigation information on the recording medium,the navigation information comprising information indicating thepresence of the second video stream.
 51. The apparatus of claim 50,wherein the controller further controls the recording unit to recordnavigation data associated with the single stream object in therecording medium.
 52. The apparatus of claim 49, wherein the recordingunit further records the first video stream and the second video streamseparately as two different stream objects.
 53. The apparatus of claim52, wherein the controller further controls the recording unit to recordnavigation data for each of the two different stream objects in therecording medium.